This invention concerns an apparatus and a method for checking value documents, in particular bank notes, and a value-document processing system.
In bank-note processing systems, properties of bank notes, such as printed image, denomination, authenticity and condition, are ascertained by capturing physical properties of the bank notes by means of sensors and evaluating the thereby generated sensor data.
Checking the condition, the so-called fitness, of a bank note involves checking whether it meets certain criteria to be able to be put back in circulation or have to be removed from circulation. Besides the degree of soiling and wear, an important criterion here is also the presence of unwanted foreign objects, usually in the form of adhesive tape or other stickers, on the bank note.
Checking the presence of adhesive tape is usually done by measuring the thickness of the bank note to be checked by means of mechanical or ultrasound thickness sensors.
From DE 10 2010 021 803 A1 it is further known to recognize by a dark-field transmission image of the bank note, if an adhesive tape was used to stick two bank note parts together. If the two bank note parts below the adhesive tape are slightly separated, their separation line appears bright in the transmission image, due to light scattering from the adhesive tape. From a bright separation line extending across the bank note one can infer that the bank note is suspicious to be a composed forgery. But if the two bank note parts being sticked together were not separated at all, no bright separation line would be detectable and thus the bank note would not be sorted out.